From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sekhar Nori Subject: Re: [PATCH v3 1/2] rtc: omap: update of_device_id to reflect latest ip revisions Date: Fri, 16 Aug 2013 21:11:30 +0530 Message-ID: <520E482A.1070504@ti.com> References: <1376653017-21935-1-git-send-email-gururaja.hebbar@ti.com> <1376653017-21935-2-git-send-email-gururaja.hebbar@ti.com> <520E341D.4080206@baylibre.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <520E341D.4080206-rdvid1DuHRBWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: Errors-To: davinci-linux-open-source-bounces-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org To: Benoit Cousson Cc: mark.rutland-5wv7dgnIgG8@public.gmane.org, a.zummo-BfzFCNDTiLLj+vYz1yj4TQ@public.gmane.org, davinci-linux-open-source-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org, rtc-linux-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org, rob-VoJi6FS/r0vR7s880joybQ@public.gmane.org, grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: linux-omap@vger.kernel.org On 8/16/2013 7:45 PM, Benoit Cousson wrote: > Hi Gururaja, > > On 16/08/2013 13:36, Hebbar, Gururaja wrote: >> The syntax of compatible property in DT is to mention the Most specific >> match to most generic match. >> >> Since AM335x is the platform with latest IP revision, add it 1st in >> the device id table. > > I don't understand why? The order should not matter at all. Yes, it should not. We are trying to work around a bug in the kernel where the compatible order is not honored (instead the order in of_match[] array matters). There were patches being discussed to fix this. > > I've tried to follow the thread you had with Mark on the v2, but AFAIK, > you've never answered to his latest question. > > Moreover, checking the differences between the Davinci and the am3352 > RTC IP, I would not claim that both are compatible. > > Sure you can use the am3352 with the Davinci driver, but you will lose > the wakeup functionality without even being notify about that. When the kernel is fixed for the bug pointed out above, this should not happen with properly defined compatible property. > > For my point of view, compatible mean that the HW will still be fully > functional with both versions of the driver, which is not the case here. I do not think that's the interpretation of compatible. Its goes from most specific to most generic per the ePAPR spec. That in itself says that 100% functionality is not expected if you don't find a match for the more specific property. > > am3352 DTS must use the ti,am3352-rtc to have the expected behavior. Yes, that's what patch 2/2 does. > Using the ti,da830-rtc version will not make the board working as > expected. So we cannot claim the compatibility. Ideally, the DT file was *always* written as compatible = "ti,am3352-rtc", "ti,da830-rtc"; even when there was no kernel support for AM3352 RTC. That way, there is no need to update the .dts[i] file. As kernel gains functionality, more features (like rtc wake) is available to users. Otherwise they get plain RTC functionality - but at least they get something instead of no RTC. Thanks, Sekhar